Field
The present disclosure relates generally to voltage controlled oscillators (VCO), and more particularly to a current re-using transformer-based dual-band VCO.
Background
Phase-locked loops (PLL) are widely used in many areas of electronics, including telecommunications as control systems. A PLL may include a VCO that generates a signal used by the PLL to match the phase of the oscillator with the phase of a received signal. The PLL may supply a voltage to the VCO to keep the phases of the received signal and the VCO signal matched. Many electronic devices, for example, mobile communication devices, operate over wide frequency ranges. However, efforts to widen the turning range of a single VCO leads to a degradation of phase noise or an increase in the power consumption.
Dual-band VCOs may employ two oscillator cores and operate in two frequency bands, for example in a range of about 2.4-4.0 GHz (low band) and a range of about 3.3-5.6 GHz (high band) and may operate in even mode (i.e., with the output signals of the two cores in-phase) or odd mode (i.e., with the output signals of the two cores out-of-phase). Conventional dual-band VCOs may have two VCO cores with re-channel metal-oxide semiconductor (NMOS) cross-coupled transistors. However, cross-coupled NMOS VCO architectures may require high operating currents. Further, conventional dual-band VCOs may become unstable, i.e., the VCO may oscillate at more than one frequency during high-band and/or low-band operation.